Our HAM Station

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New 70cm Yagi

Posted: 03 Oct 2019 08:51 AM PDT
https://stationproject.blog/2019/10/03/new-70cm-yagi/

M2 Antenna Systems 432-9WLA Specifications

We decided to replace our current 70cm yagi with a newer, higher
performance one from M2 Antenna Systems. We choose the M2 432-9WLA. The new
antenna has higher gain and a cleaner pattern that our current 70cm yagi.
It also has a longer boom.
New Yagi Ready For Installation

The first step in the project was to assemble the antenna and check its SWR
on the ground. The elements on an antenna like this typically vary by small
amounts and are usually not arranged from shortest to longest. It is
important to carefully measure each element during installation to confirm
that each element is installed at the correct location on the boom.

The folks at M2 Antenna Systems made up a custom boom support truss for us.
This is important given the potential for ice and snow accumulation that we
face here in New England. We also made up a section of LMR-600uF coax to
connect the antenna to the feedline and preamp system on our tower.
Driven Element Details

The new antenna uses a Folded Dipole style feed point. This system is
essentially a T-matching arrangement where the two sides of the driven
element are fed 180 degrees out of phase. It is important to set the
locations of the shorting blocks carefully to ensure proper operation of
the driven element and a resulting low SWR.
Yagi Going Up The Tower

Matt, KC1XX, and Andrew from XXTowers handled the installation of the new
Yagi on our tower. The installation involved climbing our 100 ft tower and
the 25 ft mast at the top to remove the old yagi and install the new one.
Note the careful rigging of the new antenna and associated feedline. This
allows the new antenna to be pulled up the tower without damaging it.


Climbing a mast is not for the faint at heart! An installation like this
one is clearly a job for experienced professionals. Andrew makes this task
look easy. Our tower camera captured some video (click on the image above
to play) of Andrews handy work.
Completed Installation

The new yagi (top antenna in the picture above) is installed on a 5 ft
fiberglass mast extension. The extension is used to ensure that the antenna
does not see a metal mast which would disrupt the antennas pattern. The
final installed height of our new yagi is a little over 125 ft. Note
Andrews good work in attaching the feedline to the mast.
432-9WLA Installed SDR Shack End

With the new yagi installed and hooked up, we made a final check of the
end-to-end SWR from the shack. The antennas SWR is very good and the 2:1
SWR bandwidth extends from the bottom of the 70cm band to almost 450 Mhz.
The new antenna is optimized for weak signal work up through the ATV
sub-band and its SWR is below 1.2:1 in this range.

Fred, AB1OC